An unusual echo behavior in the Hahn-echo 29Si NMR experiments in static samples of amorphous diamagnetic and paramagnetic silica-based materials shows the maximal echo intensity observed at echo delays calculated as 1/Δv where Δv is line width. It has been suggested that besides dead time the anomaly appears due to imperfectness of 1800 pulses, when part of the dephasing magnetization keeps dephasing after the action of these pulses, leading to the destructive interference and the intensity loss.